Qualification of a Computed Radiography System’s Exposure Range for Optimum Image Quality

With the transition from analog to digital radiography in full swing, users are gainfully embracing the technology and learning the ropes. Still, misconceptions exist with respect to evaluating proper exposure, and also with development of simple guidelines to produce images that meet basic image quality requirements. A common misconception, in particular, is that the pixel value(s) in an image’s region of interest are directly related to exposure and hence image quality. This is not quite true, as this paper will explore the relationship between pixel value and meaningful image quality measures. Without correlation to critical image quality parameters, pixel values alone can be very misleading as a gauge of proper exposure. This paper will show how these correlation procedures, recently incorporated in ASTM and EN industry standards, yield a “qualified pixel value range” as a means for the NDT practitioner to judge an image and it’s potential to meet required inspection criteria.

1. ASTM E 746, “Standard Practice for Determining Relative Image Quality Response of Industrial Radiographic Imaging Systems,” ASTM International. 2. ASTM E 2033, “Standard Practice for Computed Radiology (Photostimulable Luminescence Method),” ASTM International. 3. ASTM E 2445, “Standard Practice for Qualification and Long-Term Stability of Computed Radiology Systems,” ASTM International. 4. ISO/FDIS 17636-2, “Non-destructive Testing of Welds – Radiographic Testing – Part 2: X- and Gamma-ray Techniques with Digital Detectors,” International Organization for Standardization.
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